1. Field of Invention
The present invention relates to reflective electrooptic devices and electronic apparatuses using the same. More particularly, the present invention relates to a pixel structure of a reflective electrooptic device.
2. Description of Related Art
Related art electrooptic devices, such as liquid crystal devices, can be used as direct viewing type display devices for various apparatuses. Among the electrooptic devices described above, for example, in an active matrix liquid crystal device using TFTs as a non-linear element to provide pixel switching, as shown in FIGS. 25 and 26, pixel switching TFTs (thin film transistors) 30 and pixel electrodes 9a, each electrode being composed of a transparent conductive film, such as an ITO film, and being connected to the corresponding TFT 30, are formed on a TFT array substrate 10, and in addition, liquid crystal 50 used as an electrooptic material is held between the TFT array substrate 10 and a counter substrate 20.
In addition, in a reflective liquid crystal device, a light reflection film 8a to reflect outside light incident from the counter substrate 20 side is formed at a lower layer side of a pixel electrode 9a so that the incident light is reflected from the TFT array substrate 10 side to the counter substrate 20 side, thereby displaying an image using light emitted from the counter substrate 20 side (reflection mode).
However, in a reflective liquid crystal device, when the directionality of light reflected from the light reflection film 8a is strong, apparent viewing angle dependence occurs in which brightness of image varies depending on a viewing angle or the like. Accordingly, when liquid crystal devices are manufactured, a photosensitive resin, such as an acrylic resin, is applied to an interlayer insulating film 4 or a surface protection film 14 formed thereon, and on the surface thereof, an irregularity-forming layer 13a is formed by a photolithographic technique, thereby forming an irregular pattern 8g for light scattering on a surface of the light reflection film 8a. 
In the following example, as shown in FIG. 27, after half exposure is performed for a photosensitive resin 13 using an exposure mask 200 so that the photosensitive resin 13 is partly exposed in the thickness direction thereof, the photosensitive resin 13 is melted by heating following the development, thereby forming the irregularity-forming layer 13a having irregularities thereon in conformity with gentle changes in film thickness. Accordingly, the light reflection film 8a is formed directly on the upper layer of the irregularity-forming layer 13a. 
That is, when half exposure is performed for the photosensitive resin 13, since the photosensitive resin 13 are only partly exposed in the thickness direction thereof, after being developed, concave portions 13b are formed at positions which were exposed, and at the same time, the original thickness is maintained at positions which were not exposed. Accordingly, when the photosensitive resin 13 is melted by performing heat treatment following the development, the thickness of the photosensitive resin 13 changes gently, thereby forming the irregularity-forming layer 13a having gentle irregularities thereon in conformity with the changes in film thickness described above. As a result, even when the light reflection film 8a is formed directly on the upper layer of the irregularity-forming layer 13a, the gentle irregular pattern 8g having no edges is formed on the surface of the light reflection film 8a. 
However, in a related art liquid crystal device, since conductive films forming various wires and the TFT 30, such as a scanning line 3a, a capacitance line 3b, a data line 6a, and a drain electrode 6b, are formed at the lower layer side of the irregularity-forming layer 13a, a height difference is formed in accordance with the presence of the conductive films described above. That is, in a pixel region, the following are provided: a first region 10a in which an extending portion 1f of a semiconductor film 1a, the capacitance line 3b, and the drain electrode 6b are provided so as to form a multilayer structure; a second region 10b in which the drain electrode 6b is formed, but the extending portion 1f of the semiconductor film 1a and the capacitance line 3b are not formed; and a third region 10c in which the extending portion 1f of the semiconductor film 1a, the capacitance line 3b, and the drain electrode 6b are not formed. As a result, among the regions described above, the height differences are present in accordance with the difference in the number of conductive films formed in the region. Hence, as shown in FIG. 27, when exposure is performed for the photosensitive resin 13, since the distance from a light source to a higher position of the step thus formed is different from that to a lower position thereof, focus blurring occurs, resulting in occurrence of uneven exposure.
In addition, when exposure is performed for the photosensitive resin 13, between a region (the first region 10a, and the second region 10b) in which the conductive films are provided at the lower layer side and a region (the third region 10c) in which the conductive film is not provided at the lower layer side, a problem of uneven exposure, which is caused by the presence and non-presence of reflected light from the conductive film and the variation in intensity thereof, occurs.
When the uneven exposure described above occurs, for example, since the concave portion 13b of the irregularity-forming layer 13 may become shallower at a lower position, the irregularity-forming layer 13a cannot be formed as designed. Accordingly, it is not preferable since a desired irregular pattern cannot be formed on the surface of the light reflection film 8a. 
In addition, there is the case in which the irregularity-forming layer 13a is entirely exposed so as to form a predetermined pattern, and the irregular pattern 8g is formed on the surface of the light reflection film 8a in accordance with the presence and non-presence of the irregularity-forming layer 13a. In the case described above, since edges are formed on the irregularity-forming layer 13a, after a photosensitive resin having high fluidity is applied onto the upper layer of the irregularity-forming layer 13a to additionally form an upper insulating film, on the upper layer side thereof, the light reflection film 8a is formed. However, even in this case, when there is a height difference at the lower layer side of the irregularity-forming layer 13a, uneven exposure occurs.
In addition, when a photosensitive resin is applied onto a region in which a height difference is present, due to the planation as shown in FIG. 27, a thin film of the photosensitive resin is formed in a higher region, and on the other side, a thick film thereof is formed in a lower region. As a result, after exposure and development, when the photosensitive resin 13 is melted by heating to form a irregularity-forming layer 13a having gentle irregularities thereon, since the thin film of the photosensitive resin is formed in the higher region, the sag of the resin is small, thereby forming relatively large irregularities. On the other hand, since the thick film of the photosensitive resin is formed in the lower region, the sag of the resin becomes large, and hence the irregularities become small, resulting in a disadvantageous increase in variation of the irregularities.
The present invention addresses or solves the above and/or other problems, and provides a reflective electrooptic device and an electronic apparatus using the same. In the reflective electrooptic device described above, when the irregularity-forming layer is formed by a photolithographic technique, the conditions at the lower layer side of the irregularity-forming layer are maintained uniform so that no variation of irregular shape occurs. In addition, the present invention provides a reflective electrooptic device and an electronic apparatus using the same. In the reflective electrooptic device described above, the uniformity of a cell gap at a reflection portion is enhanced by eliminating or substantially eliminating a step formed in a reflection region so as to enhance display quality such as contrast.
Thus, a reflective electrooptic device of the present invention includes: at least one substrate; an electrooptic material held by the substrate; an insulating film; a pixel switching active element which is composed of at least one conductive film, which is provided in each pixel on the substrate, and which is electrically connected to at least one wire composed of a conductive film; a light reflection film provided in each pixel on the substrate; an irregularity-forming layer provided in a region under the light reflection film for forming a predetermined irregular pattern on a surface of the light reflection film; and at least one step-eliminating film formed in each pixel to eliminate a height difference formed by the presence of the conductive film forming the active element, the step-eliminating film being provided in a region under the irregularity-forming layer. The step-eliminating film is composed of at least one of the conductive film forming the wire, the conductive film forming the active element, and the insulating film.
In a reflective electrooptic device, when the numbers of conductive films forming various wires and an active element are different from each other, a height difference, i.e., a step corresponding to the film thickness is formed. However, in the present invention, since the step-eliminating film is formed in a region in which the number of conductive films is small, the height difference, i.e., the step is eliminated at the lower layer side of the irregularity-forming layer by this step-eliminating film. Accordingly, when the irregularity-formning layer is formed by exposing a photosensitive resin, since an apparent height difference is not present between a higher position and a lower position, uneven exposure does not or substantially does not occur. In addition, when a photosensitive resin is applied to a region in which a height difference is present, a thin film of the photosensitive resin is formed on a higher position, and on the other hand, a thick film of the photosensitive resin is formed on a lower position. Accordingly, after exposure and development are performed, when the photosensitive resin is melted by heating to form an irregularity-forming layer having gentle irregularities thereon, the sag of the resin is small at the higher position since the film of the photosensitive resin is thin, and as a result, relatively large irregularities tend to be formed. However, according to the present invention, the problem described above can also be solved. Hence, since the irregularity-forming layer can be formed as designed, a desired irregular pattern can be formed on the surface of the light reflection film. In addition, since the step-eliminating film is formed of the conductive film forming the wire, the conductive film forming the active element, or the insulating film, an additional manufacturing step is not required when the step-eliminating film is formed. Furthermore, when a height difference is present at the lower side of the pixel electrode, the thickness of an electrooptic material layer composed of liquid crystal or the like varies from region to region. However, according to the present invention, the height difference is eliminated, advantage in that display quality is improved can also be obtained.
In the present invention, the step-eliminating film is preferably composed of at least one of the conductive film forming the wire, the conductive film forming the active element, and the insulating film. When there is a region in which a conductive film is partly provided, due to the presence and non-presence of light reflected from the conductive film and variation in intensity thereof, uneven exposure tends to occur when exposure is performed. However, according to the structure described above of the present invention, since the conductive films are provided over almost the entire area of each pixel, uneven exposure does not occur. In addition, thermal conductivity is different between in a region provided with a conductive film and in a region provided with no conductive film, and hence variation in temperature tends to occur, however, when the conductive films are formed over almost the entire area, the variation in temperature can be reduced, and hence uniform curing rate of the photosensitive resin can be obtained. Accordingly, since the irregularity-forming layer can be formed as designed, a desired irregular pattern can be formed on the surface of the light reflection film. In addition, since the step-eliminating film is formed of the same layer as that for the conductive film forming the wire or the active element, an additional manufacturing step is not required when the step-eliminating film is formed.
In the present invention, for example, the step-eliminating film is formed selectively in a region in which the number of conductive films forming the active element is small, thereby eliminating the height difference.
In the present invention, when the active element comprises a thin-film transistor connected to a scanning line and a data line, which are each used as the wire, the step-eliminating film described above may include at least one of a conductive film which is composed of the same layer as that for the scanning line and is formed simultaneously therewith, and a conduct film which is composed of the same layer as that for the data line and is formed simultaneously therewith.
In addition, in the present invention, when the active element includes a thin-film transistor connected to a scanning line and a data line, which are each used as the wire, and a capacitance line is provided in each pixel to form storage capacitance, the step-eliminating film may include at least one of a conductive film composed of the same layer as that for the scanning line, a conductive film composed of the same layer as that for the capacitance line, and a conduct film composed of the same layer as that for the data line.
In the present invention, the step-eliminating film preferably has an island shape formed separately from the conductive film forming the wire or the conductive film forming the active element. According to this structure, parasite capacitance can be prevented or substantially prevented from being generated in a region in which the step-eliminating film overlaps another layer in plan view.
In the present invention, the step-eliminating film may be formed of a conductive film extending from that to form the wire or that to form the active element. For example, a film extending from an upper electrode of a capacitance portion may be used as the step-eliminating film.
Furthermore, in with another aspect of the present invention, a reflective electrooptic device includes: at least one substrate; an electrooptic material held by the substrate; a pixel switching active element which is composed of at least one conductive film, which is provided in each pixel on the substrate, and which is electrically connected to at least one wire composed of a conductive film; a light reflection film provided in each pixel on the substrate; an irregularity-forming layer provided in a region under the light reflection film to form a predetermined irregular pattern on a surface of the light reflection film; and at least one island-shaped pattern which is provided in a region under the irregularity-forming layer and which is electrically isolated from the other regions. The island-shaped pattern is composed of at least one of the conductive film forming the wire and the conductive film forming the active element.
In the present invention, the irregularity-forming layer may be composed of a photosensitive resin provided with irregularities thereon in conformity with gentle changes in film thickness, and in the case described above, the surface of the light reflection film is provided with the irregular pattern transferred from the irregularities formed on the surface of the irregularity-forming layer. The structure described above can be realized when the photosensitive resin is half-exposed using an exposure mask and is then developed to form the irregularity-forming layer.
In the present invention, the irregularity-forming layer may be composed of a photosensitive resin formed selectively into a predetermined pattern in some cases, and in the case described above, the surface of the light reflection film is provided with the irregular pattern in accordance with the presence and non-presence of the irregularity-forming layer. The structure described above can be realized when the photosensitive resin is exposed using an exposure mask and is then developed to form the irregularity-forming layer.
In the case described above, when edges are present on the irregularity-forming layer, an upper insulating film may be formed on the irregularity-forming layer. According to this structure, the surface of the light reflection film may be provided with the irregular pattern which is transferred from irregularities of the irregularity-forming layer via the upper insulating film.
In the present invention, when the electrooptic device is formed as a reflective type, the irregularity-forming layer is formed over almost the entire area of each pixel.
On the other hand, when the electrooptic device of the present invention is formed as a transflective type, the structure may be formed in which a light-transmitting window is formed in the light reflection film. In the case described above, in order to prevent or substantially prevent a decrease in light transmittance, it is preferable that the step-eliminating film or the island-shaped pattern be not formed in a region of the light-transmitting window. In the case in which the structure is formed as described above, even when uneven exposure occurs in the region of the light-transmitting window, since it is not necessary to form an irregular shape composed of a photosensitive resin in this region, problems may not occur.
In the present invention, for example, the electrooptic material may include liquid crystal.
The electrooptic device of the present invention can be applied to a display device of an electronic apparatus, such as a mobile computer or a mobile phone, for example.